Fuse Cujo with The Terminator and you get Black Mirror's 'Metalhead': a searing horror short that sees Maxine Peake's lone survivor pursued by a relentless robot hound.

The taut and terrifying episode, which, at just 38 minutes, is the most economic of Charlie Brooker's tech anthology thrillers, has received mostly positive reviews from critics, who appreciated its pared-down, gimmick-free style.

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But the version of 'Metalhead' streaming now on Netflix is quite different to the episode that Brooker had originally planned.

First off, it was director David Slade's proposal to present the episode in stark black and white. "People have suggested black-and-white episodes to us before, and we nearly did it once," Brooker has revealed. "But it just made sense for the starkness of the story. It makes the whole thing a bit more horror-movie – it's a bit like Psycho or something."

Rather than removing colour from the episode, Brooker's original intention was to strip out all dialogue.

The story of Bella (Peake) is necessarily light on dialogue, with only three human characters appearing on screen, two of whom are killed off in the episode's opening sequence.

But there are a number of key 'conversations' in the final episode, albeit most of them one-sided. Pursued by the hound, Bella uses her walkie-talkie early on in the episode to warn her loved ones that she might not make it back to them alive.

Much later, after a prolonged and brutal bout, she succeeds in destroying the robot dog, only for it to use its remaining power to stick her with a tracker, summoning dozens more of its kind. Bella confirms she's met her end and apologises for failing to return with a special something – a teddy bear for a terminally ill child, as a cruel final sting reveals.

These moments would have been missing from Brooker's planned silent episode, which was originally inspired by the 2013 survival drama film All Is Lost starring Robert Redford as a man lost at sea.

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"I'd watched All Is Lost, which is Robert Redford versus the sea for 90 minutes," Brooker explained. "I think he says 'shit' and that's it – he says that when a bit of sail breaks, or when his oar falls off...

"I enjoyed that and thought, 'I wonder...?' because partly, the beauty of doing an anthology show is that you get to reinvent the show with every episode. So I guess as a sort of challenge, or in an attempt to keep it interesting for myself, it was interesting to see...

"Now I didn't manage to have no dialogue in it whatsoever, but that was the original thought."

The finished episode also stands out for its lack of backstory and/or explanation: we never learn who built the dogs, who (if anyone) is controlling them, or even what cataclysmic event led to the collapse of human civilization.

The first draft, though, afforded us a glimpse behind the curtain. "Originally, we also showed a human operator operating the dog robot from across the ocean at his house," Brooker told Entertainment Weekly.

"There was a bit I liked, where he leaves the [control unit] while the robot is watching her while she's up in the tree and he goes and gives his kids a bath. But it felt a bit weird and too on-the-nose. It kind of felt superfluous. We deliberately pared it back."

The impetus for 'Metalhead' was, according to Black Mirror producer Annabel Jones, to create an episode "with a very simple story" which offered "unrelenting tension".

On that front, it delivers. No backstory. No gimmicks. Just no-frills terror.

Black Mirror: 'Metalhead' is available to watch now on Netflix, along with the rest of season 4.